1. Field
Disclosed embodiments relate to a joining method and a joining tool for joining members (workpieces) to be joined.
2. Related Art
Recently, development and commercialization of friction-stir joining technology have been promoted as a new joining method to be replaced for welding and brazing methods which are joining methods for workpieces (members to be worked, i.e., joined) made of metal.
The friction-stir joining, which is solid-state joining, is suitable for joining workpieces at lower temperatures than welding (weld bonding) or brazing (liquid-solid-state bonding). Thus, the friction-stir joining has advantages of causing less thermal deformation to the workpieces during joining and being relatively free of joint defects resulting from gas defects or solidification cracking due to a state change of metal in a joined portion.
The friction-stir joining is a joining method which involves preparing a joining tool of a cylindrical shape, pressing the joining tool rotating at high speed against portions to be joined of workpieces, facilitating plastic flow of the junction by frictional heat generated between the joining tool and the workpieces (more specifically, portions to be joined), thus joining the workpieces.
The joining tool includes a shoulder portion and a projection called a probe, where the shoulder portion has a large outside diameter and uniform cylindrical shape while the projection has a small diameter and projects from a tip surface of the shoulder portion. The shoulder portion and projection are located substantially on the same axis. During the joining process, with the tip surface of the shoulder portion pressed against the workpieces and the probe pushed or plunged into a joint line between the workpieces, the joining tool moves along abutting surfaces of the workpieces. The workpieces then plasticize due to heat produced by the friction with the joining tool and become joined by flowing plastically while remaining in a solid phase.
The friction-stir joining is a joining method which involves pressing the joining tool against the workpieces with a relatively large force (hereinafter referred to as a “tool load”). For example, in the case of so-called 6000 (Al—Mg—Si) Series aluminum alloys, the tool load becomes as high as approximately 3 kN to 10 kN.
The friction-stir joining, however, provides a problem in that due to the need to apply the tool load to the workpieces and because of shape or geometry of the joining tool, it is difficult to join portions having complicated shapes such as curved shapes, rectangular shapes, or the like at an edge portions of the workpieces, i.e., joint portions having non-flat shapes. In addition, the friction-stir joining may provide a problem in that a probe pull-out hole is left in a jointed end portion.
To deal with the defects mentioned above, there is also provided a joining method which involves forming tabs or extension portions at end portions of the workpieces (more specifically, portions to be joined), performing friction-stir joining by utilizing the tabs or extension portions as a joint start portion or joint end portion, subsequently cutting off the tabs or extension portions by using another machine tool, thereby joining the joint portions of the workpieces having a non-flat shape without leaving a probe pull-out hole (for example, refer to Patent Document 1: Japanese Patent Laid-Open Publication No. 10-71477).
On the other hand, in the friction-stir joining method, there may cause a case in which, after passing through the junction of the workpieces, the joining tool might produce burrs on a surface of the joined portion. The burrs are undesirable in applications which require the surface of the junction to be smooth (e.g., an assembly in which the surface of the junction is used as a mating surface) or in applications which require an attractive appearance (e.g., an elaborately designed surface). Thus, there is also provided a friction-stir joining method which is capable of removing burrs from the surface of a junction concurrently with the friction-stir joining working using a joining tool equipped with a cutting blade adapted to rotate integrally with the joining tool (for example, refer to Patent Document 2: Japanese Patent Laid-Open Publication 2003-126973, in addition to Patent Document 1).
The conventional joining method which performs friction-stir joining using tabs or extension portions of the workpieces as the joining working start portion or joining working end portion need to cut off the tabs or extension portions using another machine tool after the joining. In this conventional method, because of the need to cut off the tabs or extension portions using another machine tool after the joining, compared to methods which do not need a process for cutting off tabs or extension portions, the conventional joining method requires additional time and labor, for example, to make a setup change from the joining apparatus to a cutting machine tool in order to cut off the tabs or extension portions, which may result in increasing in the cost of the joined product.
On the other hand, in the case of the friction-stir joining method capable of removing burrs from the surface of the junction concurrently with friction-stir joining working to the workpiece using a joining tool equipped with a cutting blade adapted to rotate integrally with the joining tool, although the method may provide a smooth junction, the method does not consider the necessity of cutting off the tabs or extension portions with the cutting blade when performing friction-stir joining using the tabs or extension portions of the workpieces as the joint working start portion or joint working end portion.
Moreover, since the friction-stir joining method cuts off burrs with the cutting blade, chips adhere to the workpieces or joined product, joining tool, and friction-stir joining apparatus, additional time and labor are then required for cleaning or other chip removal measures, leading to further increasing in the cost of the joined product.